Nanomechanical switches and circuits

ABSTRACT

A highly miniaturized nanomechanical transistor switch is fabricated using a mechanical cantilever which creates a conductive path between two electrodes in its deflected state. In one embodiment, the cantilever is deflected by an electrostatic attraction arising from a voltage potential between the cantilever and a control electrode. In another embodiment, the cantilever is formed of a material with high magnetic permeability, and is deflected in response to complementary magnetic fields induced in the cantilever and in an adjacent electrode. The nanomechanical switch can be fabricated using well known semiconductor fabrication techniques, although semiconductor materials are not necessary for fabrication. The switch can rely upon physical contact between the cantilever and the adjacent electrode for current flow, or can rely upon sufficient proximity between the cantilever and the adjacent electrode to allow for tunneling current flow.

FIELD OF THE INVENTION

[0001] This invention relates generally to submicron switching devicesand more specifically to a nanomechanical switch using a deformablecantilever element.

BACKGROUND OF THE INVENTION

[0002] A significant factor in the electronic revolution has been thesteady evolution of increasingly smaller integrated circuit geometriesfor the fabrication of semiconductor switching transistors. Typicalfeature sizes have been reduced from tens of microns in the earlyeighties, to roughly ten microns in the mid eighties, to below onemicron in the mid nineties, until minimal lateral feature sizes of assmall as 0.15 microns are not uncommon today. In addition to the obviousadvantage of allowing for more transistors on a single chip, the smallerdevice geometries require less operating power and provide for fasterswitching speeds.

[0003] The preferred technology for state of the art submicronsemiconductor devices is metal oxide silicon (MOS) transistors, whichdevices have historically allowed for ready scaling to smaller sizes asnew submicron fabrication technologies are developed. MOS technology isapproaching practical scaling limits, however, and it is projected thatconventional MOS transistors cannot be scaled beyond 0.07 micrometers intheir minimum feature size. These practical limitations include wellknown semiconductor phenomena, such as hot electron injection, gateoxide tunneling, short channel effects, and sub-threshold leakage thatarise when the features of the transistor are too close together toallow proper turn-on and turn-off behavior.

[0004] It is also essential in military and space applications ofdigital electronics to prevent ambient nuclear or solar radiation fromaffecting the dynamic operation of switching devices. Switches based onsemiconductor materials are vulnerable to such radiation effects,however.

[0005] Therefore, a need exists for a submicron switching device thatdoes not consume excessive power, that has a fast switching responsetime, and that can be scaled beyond the current practical limitationsfor semiconductor switching transistors. The need also exists for asubmicron switching device that is largely unaffected by high doses ofparticle, electromagnetic or other radiation.

SUMMARY OF THE INVENTION

[0006] In one aspect, the present invention provides a nanomechanicalswitch comprising a substrate and first, second and third electrodesformed on the substrate. The third electrode includes a cantilevermember extending over the first and second electrodes. A voltage sourceis coupled between the first and third electrodes, wherein thecantilever member has an undeflected state when no bias is appliedbetween the first and third electrodes, and a deflected state when abias is applied between the first and third electrodes.

[0007] In other aspects, the invention provides for logical circuitsformed of one or more such nanomechanical switches being connectedtogether. In another aspect, the present invention provides for anintegrated circuit comprising a substrate, a power conductor, a groundconductor, an input terminal and a logic circuit. The logic circuitcomprises a plurality of nanomechanical switches, at least onenanomechanical switch being coupled to said power conductor, and atleast one nanomechanical switch being coupled to said ground conductor.Each such nanomechanical switches comprise a first electrode, a secondelectrode, and a third electrode having a cantilever member extendingsubstantially parallel to the substrate and extending over the first andsecond electrodes. The logic circuit further comprises a voltage sourcecoupled between the first and second electrodes, wherein the cantilevermember has an undeflected state when no bias is applied between thefirst and third electrodes, and a deflected state when a bias is appliedbetween the first and second electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The above features of the present invention will be more clearlyunderstood from consideration of the following descriptions inconnection with accompanying drawings in which:

[0009]FIGS. 1a and 1 b are a cross section of a first preferredembodiment switch in the open state and the closed state, respectively;

[0010]FIGS. 1c and 1 d are plots of the response time of a firstpreferred embodiment nanomechanical switch;

[0011]FIGS. 2a through 2 j illustrate a preferred embodiment process formanufacturing a nanomechanical switch 10;

[0012]FIGS. 3a through 3 c illustrate a second preferred embodimentnanomechanical switch;

[0013]FIGS. 4a through 4 d illustrate a third preferred embodimentnanomechanical switch;

[0014]FIGS. 5a through 5 c illustrate multiple nanomechanical switchescomprising a common drain circuit;

[0015]FIGS. 6a through 6 g illustrate a preferred embodimentcomplementary pair nanomechanical switch circuit;

[0016]FIGS. 7a and 7 b illustrate a second preferred embodimentcomplementary pair nanomechanical switch circuit;

[0017]FIGS. 8a and 8 b illustrate a preferred embodiment complementaryinverter;

[0018]FIGS. 9a through 9 c illustrate a preferred embodiment circuit;

[0019]FIG. 10 is a graph plotting tunneling current as a function oftunneling distance for preferred embodiment nanomechanical devices;

[0020]FIGS. 11a and 11 b illustrate a fourth preferred embodimentnanomechanical switch;

[0021]FIGS. 12a and 12 b illustrate a fifth preferred embodimentnanomechanical switch; and

[0022]FIG. 13 illustrates a preferred embodiment integrated circuitcomprised at least in part of nanomechanical switches.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0023] The making and use of the various embodiments are discussed belowin detail. However, it should be appreciated that the present inventionprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

[0024] The present invention provides for a nanomechanical switch 10 asshown in FIGS. 1a and 1 b. The switch is formed on substrate 2,preferably formed of a bulk semiconductor, but alternatively formed ofany suitable non-conductive substrate such as glass, sapphire, ceramic,plastic, or the like. With a ceramic substrate, it would be particularlyadvantageous to use a glazed ceramic in order to obtain a smooth enoughsurface for further processing of the device features. Quartz would alsomake a good substrate because of its relatively low dielectric constantcompared to material such as semiconductor, in order to preventformation of unwanted capacitance with the substrate. In otherembodiments, the switch may be formed on an insulating layer formed onthe surface of substrate 2. In the case of the semiconductor substrate,a silicon dioxide layer could be formed prior to further processing.

[0025] Formed atop substrate 2 are metallic pads 6 and 8, referred toherein as the gate and drain, respectively. A source 4 is formed as anelongated metallic member 14 that is cantilevered over drain 8 and gate6, and separated from them by thickness t₁ and t₂, respectively. Notethat drain pad 8 is thicker (i.e. taller) than gate pad 6. This is toprevent cantilever 14 from contacting gate pad 6 when in its deflectedstate, as will be explained in further detail below.

[0026] In the first preferred embodiment, the dimensions for gate 6 anddrain 8 are 0.1 microns by 0.1 microns. The dimension for drain 8 ispreferably 0.05 microns by 0.1 microns. The dimensions for oxide feature3, which acts as a hinge support, are preferably approximately the sameas for drain 8. As will be apparent to one skilled in the art whentaking the teachings contained herein into account, variations to thepreferred embodiments can be made depending upon the design parametersto be achieved.

[0027] Formed atop and supported by oxide feature 3 is source 4,including cantilever 14 which extends substantially horizontally outfrom oxide feature 3 over drain pad 8 and gate pad 6. Note thatcantilever 14 is spaced apart from the top of drain pad 8 when in itsnormal or undeflected state, by a switch gap, denoted as t₁. In thepreferred embodiments, t₁ is about 20 to 40 angstroms in the open orundeflected state. Preferably t₂ should be about 10 to 20 angstromsgreater than t₁, or about 30 to 50 angstroms. Although shown asprojecting out horizontally, in alternative embodiments, cantilever mayproject out from source pad 4 at an angle to substrate 2 in order to,e.g. increase or decrease the normal state gap between cantilever 14 anddrain pad 8. Also contemplated within the scope of the invention, is ananomechanical switch that is formed normal to the plane of thesubstrate, such as may be formed on the sidewall of a deep trench in thesubstrate or a deep trench formed in a layer of material deposited onthe substrate.

[0028] Also shown is voltage source 12 connected between source pad 4and gate pad 6. In FIG. 1a, voltage source 12 is at 0 V. Source 4 andhence cantilever 14 are at zero bias with regard to gate pad 6. In FIG.1b, however, voltage source 12 has been set to a positive value causinggate pad 6 to be positively biased with respect to source pad 4 andcantilever 14. This bias causes an electrostatic attraction between gatepad 6 and cantilever 14, thus pulling cantilever 14 downwards. As shown,because gate pad 6 is below the height of drain pad 8, cantilever 14contacts drain pad 8 as a result of the attractive pull. In this way, anelectrical circuit is completed between source pad 4 and drain pad 8.Note that the electrostatic attraction between gate pad 6 and cantilever14 persists even when current flows from source 4 through cantilever 14to drain 8. Note also that the electrostatic attraction is independentof the polarity of the voltage between source 4 and gate 6.

[0029] A brief discussion about the performance characteristics of thepreferred embodiment switch is now provided. In the first preferredembodiment, cantilever 14 is constructed of aluminum and has a thicknessof approximately 25 nm, a width of approximately 100 nm and a length ofapproximately 200 nm. Such a cantilever would have a volume of 5E-16 ccand a mass of about 1.35E-18 Kg. Assume the desired switching frequencyis 2 GHz, then the switch response time must be 500 ps. This responsetime requires an approximate acceleration of the cantilever 14 at therate (2*t₁)/T² where t₁ is the switch gap (the distance betweencantilever 14 and drain pad 8), and T is the response time. For a switchgap of 4 nm, and a response time of 500 ps, the required accelerationwould be 3.2E10 m/s². Under such acceleration, the velocity ofcantilever 14 at the point it contacts drain pad 8 would beapproximately (2*t₁)/T or 16 m/s. Obviously, even faster switching timescould be obtained, depending on the attractive force between cantilever14 and gate pad 6, the mass of cantilever 14, the switch gap t₁, and theamount of voltage available to bias gate pad 6. For instance, the workthat must be extended to move preferred embodiment cantilever 14(mass*acceleration*distance) is 1.7E-16 Joules (1.35E-18 Kg*3.2E10 m/s²*4 nm). This compares to the highest speed conventional semiconductorswitches, which require switching energies in the range of tens offemtojoules. Assuming 2 watts of chip power were available, preferredembodiment cantilever 14 can be continuously switched at 2 GHz with anoperating power of 1.7E-16*2E9=0.34 microwatts. This would allow2/0.34E−6=6 million such switches to operate simultaneously with the 2watt power budget.

[0030] Note that because of the inherent resiliency of cantilever 14,the switch will return to its open state (as shown in FIG. 1a)substantially as rapidly as the cantilever reaches its closed state. Nobiasing or voltage is required to open the switch; cantilever 14 willreturn to its undeflected state due to its spring constant once the gatevoltage is removed.

[0031] The approximate required gate voltage for voltage source 12 canreadily be determined from the formula F=CV²/t₂ where F is the requiredforce to operate the switch, V is the gate voltage, C is the gatecapacitance, i.e. the capacitance between gate pad 6 and cantilever 14,and t₂ is the distance between gate pad 6 and cantilever 14. In theabove described configuration, the gate capacitance C is about 1.8E-17Farads (based on the dimensions of the cantilever and an underlying gateof roughly 100 nm by 100 nm), and the distance d is about 5 nm. A gatevoltage of about 3.5 volts would be sufficient to fully deflectcantilever 14, assuming a cantilever vertical force (restoring force)constant of less than 16 Newtons per meter. Even lower gate voltage canbe used if slower switching speeds are acceptable or if a lighter orless stiff cantilever is employed.

[0032] Disregarding contact resistance, the on-state resistance of theswitch is about one ohm, which compares very favorably with the on-stateresistance of about 92E3 ohms that would be expected for a 0.1micrometer wide transistor using conventional MOS technology. With sucha low resistance, the RC delay of the gate will be on the order of2.2E-17 F*20E3 ohms=0.4 psec.

[0033]FIGS. 1c and 1 d demonstrate the response time of switch 10 goingfrom an open state (cantilever undeflected) to a closed state(cantilever deflected) for a 3 volt gate voltage and a 2 volt gatevoltage, respectively. Note that the cantilever deflects the full 40angstroms (i.e. closes the switch gap) in roughly 400 picoseconds inFIG. 1c when a 3 volt gate voltage is applied. The response timeincreases to about 900 picoseconds at the lower gate voltage of 2 volts,as shown in FIG. 1d.

[0034]FIGS. 2a through 2 j illustrate a preferred embodiment process formanufacturing a nanomechanical switch 10. In FIG. 2a, two metal layers22 and 24 have been formed atop substrate 2. In the preferredembodiments, metal layer 22 is formed of platinum and metal layer 24 isformed of aluminum. Each layer is preferably 500 Angstroms thick and canbe thermally deposited. Alternative deposition techniques such assputtering, vapor deposition, and the like, as well as epitaxial growthof metal layers 22 and 24 are also contemplated.

[0035] As shown in FIG. 2b, a photoresist layer 26 is patterned atopmetal layer 24 with patters 28 and 29. Pattern 28 is formed in order tocreate an etch between islands 30 and 32 after an etch step has beenapplied, as shown in FIG. 2c. Pattern 29 in photoresist layer 26 isincluded in order to form island 30 symmetrically. In a separate processstep, not shown, islands 30 and 32 are covered with a photoresist layerand the portion of metal layers 22 and 24 lying to the left of metallicisland 30 is exposed to an etchant and etched away. The resultingstructure is that illustrated in FIG. 2c. In an alternative embodiment,pattern 29 could be omitted and islands 30 and 32 formed without theintervening steps associated with pattern 29.

[0036] In a next process step, island 30 is covered with photoresistlayer 36, as shown in FIG. 2d and island 32 is exposed to an etchantthat selectively etches away metal layer 24, while leaving metal layer22 intact, as shown in FIG. 2e. In the preferred embodiment structure,HCl or KOH etchants may be employed to selectively etch away thealuminum layer 24 without etching platinum layer 22. As illustrated inFIG. 2f, islands 30 and 32 are then covered with a deposited oxide layer32, such as silicon dioxide, and oxide layer 32 is then subjected to achemical mechanical polish step to form a smooth, planar surface 40, asshown in FIG. 2g. In other embodiments, a flowable oxide may be employedto form first oxide layer 38, which has the advantage of forming arelatively planar surface. Alternatively, plasma oxides could beemployed. A second oxide layer 42 is then formed atop the planar surface40, as shown in FIG. 2h. Second oxide layer 42 can be formed of the samematerial as first oxide layer 32, although this is not necessary. In thepreferred embodiments, second oxide layer 42 is selected for providinggood adhesion to metal layer 44 (FIG. 2i). For instance, if metal layer44 is to be formed of aluminum, oxide layer 42 may be selected asaluminum oxide to provide good adhesion.

[0037] As will become apparent below, the thickness of second oxidelayer 42 defines the switch gap t₁. In other embodiments, second oxidelayer 42 could be eliminated if first oxide layer 38 could be grown ordeposited with enough control and precision to form first oxide layer 38with the desired thickness t₁ above island 30.

[0038] Metal layer 44 is then deposited atop second oxide layer 44 toform source 4, including cantilever 14. As will be apparent to oneskilled in the art, source 4 and cantilever 14 can be formed throughselective deposition of metal layer 44, or through subsequent mask andetching steps. Metal layer 44 is preferably aluminum or copper dopedaluminum. The desired properties of metal layer 44 are low resistance,high resilience, and compatibility with metal layer 24 which forms thetop surface of drain 8 (shown as island 30 in FIGS. 2c through 2 k).Alternatively, metal layer 44 could be formed of platinum or some otherrefractory metal such as gold, nickel, paladium, tungsten or the like.Care should be taken in the selection of metal layer 24 and metal layer44 that the selected metals do not tend to form alloys with each otherand do not tend to stick together (from thermal bonding) as cantilever14 (metal layer 44) comes into contact with drain 8 (metal layer 24).Another advantage of refractory metals is that very thin films can beformed, while still being a continuous film. In the preferredembodiments, metal layer 24 and metal layer 44 are formed of the samerefractory metal, for the reasons discussed above. In other embodiments,other conductive materials, such as doped carbon or doped semiconductor,could be utilized in place of metal layers 22, 24, 44.

[0039] Also contemplated within the scope of the invention is laminatedmetal layers 22, 24, and 44, in which multiple sub-layers of differentmetals (such as platinum and aluminum) are sequentially deposited toform the metal layer. Laminated metal sub-layers tend to minimizewarping and deformity of the layer, thus allowing tight tolerances inthe switch gap t₁ and also in t₂. The smaller the switch gap t₁, thelower the operating voltage required to switch nanomechanical switch 10from its open to closed state because of the higher field beinggenerated across the gap.

[0040] In a subsequent process step, oxide layers 38 and 42 aresubjected to an etchant such as CF₄+O₂ or other well known plasmaetchants. The desired etchant will provide good lateral etching of theoxide layers in order to etch oxide layers 38 and 42 back beneath metallayer 44, leaving a gap between metal layer 44 and island 32, andbetween metal layer 44 and island 30, as shown in FIG. 2j. The resultingstructure provides for gate 6 formed from island 32, drain 8 formed fromisland 30, and source 4 including cantilever 14 formed from metal layer44. Although not shown for clarity, appropriate interconnects will alsobe provided in order to connect resulting switch 10 with other circuitcomponents, including voltage source 12 between source 4 and drain 6.

[0041]FIGS. 3a and 3 b illustrate in cross section and FIG. 3cillustrates in perspective view, a second preferred embodimentnanomechanical switch 10, in the open and closed states, respectively.In the second preferred embodiment, source 4 is formed of a metallicisland upon which is formed cantilever 14, and gate 6 is formed betweensource 4 and drain 8. As will be apparent to one skilled in the art, theprocessing required for forming the second preferred embodimentstructure is similar to the first preferred embodiment structure,although three metallic islands would be formed, one each for the source4, gate 6 and drain 8. Two advantageous features of the first preferredembodiment bear noting. First, by having the gate 6 spaced apart fromthe fulcrum for cantilever 14, greater torque can be obtained when gate6 applies an electrostatic force on cantilever 14. Another advantage isthat the larger gap between gate 6 and cantilever 14 may allow for morerapid and uniform etching of oxide layers 38 and 42, then would beprovided with the smaller gap between drain 8 and cantilever 14 of FIGS.3a and 3 b.

[0042] Various alternative embodiment switches and circuits will now bedescribed with reference to FIGS. 4a through 9 c. For instance, FIG. 4aillustrates in perspective view an alternate layout for nanomechanicalswitch 10 in which the gate 6 and drain 8 are both positioned under andnear the free end of cantilever 14. FIG. 4b illustrates in elevationview from the side, and FIG. 4c illustrates in elevation view from thefree end of the cantilever, the same switch 10. FIG. 4d provides aschematic representation of the device.

[0043]FIG. 5a provides a perspective view and FIG. 5b an elevation viewof a common drain, two switch circuit 10 and 10′, as illustratedschematically in FIG. 5c. The circuit has two sources 4 and 4′,including two cantilevers 14 and 14′, either of which will makeelectrical contact with common drain 8, under the control of gate 6 or6′, respectively. Only one source 4′ and one gate 6′ is illustrated inFIG. 5b, as the other source 4 and other gate 6 will be obscured whenseen from the side. FIG. 5c illustrates the common drain circuitschematically.

[0044]FIGS. 6a through 6 g illustrate a nanomechanical switch configuredto provide a CMOS type complementary response, as illustratedschematically in FIGS. 6d and 6 g. In FIG. 6a the switch 10 is shown inperspective. Control gate 6 is shown underlying cantilever 14 but inthis embodiment cantilever 14 is electrically coupled to output pad 50,rather than being formed from source pad 4. Instead source pad 4 isformed beneath the free end of cantilever 14 and drain 8 is formedoverlying the free end of cantilever 14. FIGS. 6b and 6 c illustrate theswitch 10 of FIG. 6a in elevation view from the side and end-on viewfrom the free end of cantilever 14, respectively. As shown, in theundeflected state (i.e. gate 6 being unbiased with respect to cantilever14), cantilever 14 is held against drain 8 by the inherent springtension of cantilever 14. Output pad 50 is thus connected to drain 8 andcurrent will flow from drain 8 to output 50. As shown in FIGS. 6e and 6f, when a control voltage is applied to gate 6, an electrostaticattraction between gate 6 and cantilever 14 deflects cantilever 14downward, breaking its electrical contact with drain 8 and bringingcantilever 14 into electrical contact with source 4. In this casecurrent will flow from source 4 to source 50 (or in the other directiondepending on the respective voltage levels on source 4 and output 50).In this way, output 50 can be electrically connected to either the drain8 or the source 4. Setting drain voltage equal to a logical high and thesource voltage equal to a logical low will result in a CMOS type circuitas is known in the art.

[0045] An alternative CMOS type circuit is illustrated in perspective inFIG. 7a and in plan view (i.e. top down view) in FIG. 7b. Asillustrated, two gates 6 and 6′ are positioned on either side of alaterally moving cantilever 14 which is connected to output 50. Notethat unlike the previously discussed embodiments in which cantilever wasdeflected normally to the plane of substrate 2, in the embodiment shownin FIGS. 7a and 7 b, cantilever 14 moves in a plane substantiallyparallel to the plane of substrate 2. In an undeflected state, i.e. whenneither gate 6 nor gate 6′ is biased with respect to cantilever 14, thecantilever will be positioned between gate 8 and source 4, but inelectrical contact with neither. When a control voltage is applied tothe first gate 6, cantilever will be deflected toward it and will comeinto electrical contact with drain 8, thus allowing current to flowbetween drain 8 and output 50. On the other hand, when a control voltageis applied to the second gate 6′, cantilever 14 will be deflected towardsource 4, thus electrically connecting source 4 and output 50 anddisconnecting drain 8 and output 50. Note that, as best shown in FIG.7b, the gates 6 and 6′ are spaced further apart from cantilever 14 thanare source 4 and drain 8 in order to ensure that cantilever 14 comesinto electrical contact with source 4 and drain 8 and does not short outagainst or come into electrical contact with gates 6 and 6′. Anadvantage provided by this embodiment is that the output 50 can be putin a high impedance state, i.e. when neither gate 6 nor gate 6′ isbiased with respect to cantilever 14, or when both gates 6 and 6′ areessentially equally biased with respect to cantilever 14.

[0046] Yet another device is illustrated in FIGS. 8a (plan view) and 8 b(schematically), where two cantilevers 14 and 14′ are employed to form acomplementary inverter. A single gate control voltage is tied to twogates 6 and 6′ associated with cantilevers 14 and 14′ respectively. Theillustrated circuit will provide an inverted signal in response to aninput signal G1 being applied to gates 6 and 6′. As shown, eachcantilever has a fixed voltage source placed opposite its respectivegate. Fixed voltage source 52 is adjacent cantilever 14 opposite fromgate 6 and is tied to a 0V. Fixed voltage source 52′ is adjacentcantilever 14′ opposite from gate 6′ and is tied to 1V. Note thatvoltage sources 52 and 52′ are spaced further from cantilevers 14 and14′, respectively, than are gates 6 and 6′, respectively. Assume a zerovolt (or logical low) gate voltage G1 is input to the circuit. Gate 6will electrostatically attract cantilever 14, which is held at a onevolt via source 4 and will deflect cantilever 14 to contact output pad50. Cantilever 14′, being held to a zero volt level will not beattracted to gate 6′ when it is at a logical low. On the other hand,when gate voltage G1 is set to a logical high voltage, cantilever 14′will be attracted and deflected toward gate 61, thus connecting output50′ to drain 8 at zero volts. At the same time, cantilever 14, beingheld at a logical high level by source 4, will no longer be deflectedsufficiently to contact gate 6. FIG. 8b schematically illustrates thecircuit.

[0047] Yet another device is illustrated in FIGS. 9a through 9 c. Inthis embodiment, a logical AND function is achieved through seriallyganging two nanomechanical switches 10, as shown in perspective in FIG.9a. In this embodiment, the drain of the first switch is connected tothe source of the second switch. The first source 4 is deflected tocontact common source/drain 54 when first gate 6 is high (i.e. biasedwith respect to cantilever 14 of first source 4). Common source/drain 54is controlled by second gate 6′ and connects to drain 8 when gate 6′ ishigh. A logical input at drain 8 will be coupled to source 4 only whenboth gates 6 and 6′ are high. FIG. 9b schematically illustrates thecircuit of FIG. 9a, and FIG. 9c provides a truth table for the circuitshowing its logical AND function.

[0048] In many applications, the gate to source voltages that are usedto operate the cantilever will be of the same magnitude as those appliedbetween the source and drain. It is necessary to arrange the dimensionsof the gate and drain such that the electrostatic force of the gate tothe cantilever is sufficiently greater than the force between the drainand cantilever so as to prevent the cantilever from being deflectedsimply by the voltage applied between the source and drain pads.Likewise, the restoring force of the cantilever must be sufficientlygreater than the electrostatic force between the drain and thecantilever when the cantilever is deflected onto the drain so as toprevent the cantilever from remaining in the deflected state when thegate voltage is removed.

[0049] The electrostatic force between two roughly parallel metals isapproximately CV²/d where C is the capacitance between the metals, V isthe potential difference between the metals, and d is the separationbetween them. Since in many applications, V and d will be similar forthe gate and drain voltages and for the cantilever separations, one wayto ensure that the drain to cantilever force is substantially less thanthe gate to cantilever force is to ensure that the capacitance betweenthe gate and the cantilever is substantially greater than the drain tocantilever capacitance. This is preferably accomplished by making thegate pad (electrode) much larger in surface area than the drain pad. Itis also noted that locating the drain pad between the cantilever hingeand the gate pad also reduces the effect of the drain voltage relativeto the gate due to the greater leverage of the gate force on thecantilever relative to the drain force.

[0050] In the above described embodiments, it has been assumed thatphysical contact between the cantilever and the drain was required inorder to generate source to drain current. As will be described in thefollowing paragraphs, actual contact is not required because the devicecan take advantage of electron tunneling. Electron tunneling is aquantum phenomenon in which an electron will cross an insulatingbarrier, such as a vacuum gap or air gap, provided the barrier issufficiently thin compared to the quantum or DeBroglie wave length ofthe electron in the barrier material.

[0051] Referring now to FIG. 10 in conjunction with FIG. 3a, a graphshows the relationship between the tunneling current between cantilever14 and drain 8 as a function of the distance between the cantilever andthe drain. The tunneling current is a function of the surface areabetween the electrodes, the work function of the electrodes, the voltagebetween the cantilever and drain, and the distance between them. Assumethe dimensions of drain pad 8 are 500 angstroms by 1000 angstroms theswitch gap t₁ varies from 20 angstroms in the undeflected state to 5angstroms in the deflected state, and that the cantilever to drainvoltage is 2 volts. For the preferred embodiment switch in which the gapmaterial is vacuum, the work function for aluminum electrodes is 4volts. The relationship between tunneling current and switch gap t₁ isshown in FIG. 10. In the undeflected state, (i.e. t₁ at 20 angstroms)the tunneling current between cantilever 14 and drain 8 would be on theorder of 10E-18 amps—effectively an open circuit. In fact, this amountof off state tunneling current is much less than the off state leakagecurrent associated with current MOS transistors by many orders ofmagnitude. Note also that an undesired tunneling current may also occurbetween cantilever 14 and gate 6. The distance between cantilever 14 andgate 6 is preferably 40 angstroms, however. By extrapolating the plot ofFIG. 10, it will be clear that the tunneling current crossing the 40angstrom gap will be essentially non-existent.

[0052] By contrast, when the cantilever is brought close to drain 8 (say5 angstroms), in response to control gate 6, the tunneling currentincreases exponentially to approximately 1 microamp—clearly sufficienton-state current for typical logic circuits, even though cantilever 14and drain 8 are not in contact.

[0053]FIGS. 11a and 11 b illustrate a preferred embodiment switch whichtakes advantage of the tunneling effect to allow for a lubricating layerbetween cantilever 14 and drain 8 in order to minimize the risks ofmechanical failure, alloy formation, thermal bonding, and the likearising from metal to metal contact. FIGS. 11a and 11 b are essentiallythe same as FIGS. 3a and 3 b, but with the addition of lubricating layer58 formed on the top surface of drain 8. Lubricating layer 58 ispreferably an oxide or polymer insulating layer that of approximately 5angstroms thickness. This layer provides a buffer between cantilever 14and drain 8 when the cantilever is in its deflected state. Even thoughlayer 58 is an insulating layer, as discussed above, the switch, whencantilever 14 is deflected, will be in an on state because of thetunneling current flowing across the 5 angstrom layer. In fact, becausethe work function for an oxide or polymer is less than that for vacuum,more tunneling current will flow across layer 58 than would flow acrossa vacuum gap of similar thickness. Thus many different insulators orconductors could be selected for the lubricating layer 58 withoutreducing the performance relative to a vacuum insulator. Any of theabove described embodiments will also exhibit the desired tunnelingphenomenon with appropriately chosen materials and dimensions.

[0054] The above embodiments have been essentially “MOS analogs” inwhich the controlling signal is a gate voltage. A “bipolar analog”embodiment controlled by current will now be described with reference toFIGS. 12a and 12 b. As shown in FIG. 12a, switch 60 comprises an emitter64 electrode including a cantilever 74, and a base electrode 66 andcollector electrode 68. Current flowing through base electrode 66creates a magnetic field surrounding the electrode, as shown in FIG.12b. This magnetic field induces a magnetic field in emitter electrode64, and in particular cantilever 74 and also in collector electrode 68.The induced magnetic fields in cantilever 74 and collector 68 areoriented with the polarity of the field created by current in baseelectrode 66. As illustrated, the induced magnetic north pole incantilever 74 will be complementary to the induced magnetic south polein collector electrode 68, thus resulting in a magnetic attraction thatwill cause cantilever 74 to deflect toward collector 68. It should benoted that the magnetic field emanating from base electrode 66 decreasesroughly with the distance r from the electrode (1/r). The distancebetween base electrode 66 and cantilever 14 must be fairly smalltherefore, in order to sufficient a magnetic field to be induced incantilever 14 and collector 68 to overcome the natural resiliency ofcantilever 14.

[0055] In the preferred embodiment magnetic switches, both cantilever 74and collector 68 should be formed of material with magnetic permeabilitymuch greater than one, such as ferro-magnetic or para-magneticmaterials, so as to have a strong magnetic field induced within them.Examples would include iron, nickel, cobalt, paladium, conductive alloysof these materials, and the like. Note that the use of multi-layermaterials may be particularly advantageous for obtaining both desirableconductivity and magnetic permeability in the cantilever, and thecollector and emitter. Preferably the multi-layer material would providefor a high conductivity surface layer, such as gold, covering a bulkmaterial with a high magnetic permeability, such as nickel.

[0056] An advantageous feature of the magnetic embodiments is that themagnetic attraction is a function of the current in base electrode 66,as opposed to being a function of voltage. Therefore, magneticallyactivated transistors can be built with very low operating voltages.Base electrode 66 is preferably made of gold or other material with verylow resistivity in order to minimize the voltage required to generatebase current. Alternatively, by constructing base electrode 66 out of asuperconducting material, no energy would be consumed by the device inthe steady state, because no voltage would be required to maintain basecurrent.

[0057] Many variations to the described embodiments will be apparent toone skilled in the art with the benefit of the teachings containedherein. For instance, the various switches and circuits described hereincan be combined to form logical circuits and devices. The switches andcircuits described herein can be fabricated using known semiconductorprocessing techniques, and can hence be formed on a common substratewith classical CMOS or NMOS switches and circuits. Whereas theembodiments have been described with respect to a vacuum gap, Argon orsome other noble gas could also be employed. An air ambient could alsobe employed if care is taken minimize effects such as corrosion.

[0058]FIG. 13 illustrates an integrated circuit 100 embodying aspects ofthe invention. The integrated circuit includes a substrate 102 uponwhich is formed various circuit components. Signals can be supplied toand received from integrated circuit 100 by way of input/output ports106. Power is supplied to integrated circuit 100 by way of power port108 and ground port 110, to which are coupled power conductor 112 andground conductor 114, respectively for supplying power to circuitcomponents. Included in the circuit components is nanomechanical logiccircuit 116, Nanomechanical logic circuit 116 is formed of a series ofinterconnected nanomechanical switches as described above. Also shown inFIG. 13 is memory array 118, preferably also formed of nanomechanicalswitches configured as memory cells. Preferably, all circuits formed onintegrated circuit 100 are fabricated using nanomechanical transistorsin order to provide the benefits of speed, size, power savings, andradiation survivability discussed above. In some embodiments, however,semiconductor logic 120 could also be formed on substrate 102 using wellknown MOS, CMOS or bipolar semiconductor processes.

[0059] Various other modifications and combinations of the illustrativeembodiments, as well as other embodiments of the invention, will beapparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A nanomechanical switch comprising: a substrate;a first electrode formed on the substrate; a second electrode formed onthe substrate; a third electrode having a cantilever member extendingover the first and second electrodes; a voltage source coupled betweenthe first and third electrodes, wherein the cantilever member has anundeflected state when no bias is applied between the first and thirdelectrodes, and a deflected state when a bias is applied between thefirst and third electrodes.
 2. The nanomechanical switch of claim 1wherein the cantilever member contacts the second electrode when in thedeflected state.
 3. The nanomechanical switch of claim 1 furthercomprising a lubricating layer formed atop of the second electrode. 4.The nanomechanical switch of claim 1 wherein the second electrode isbetween the first and third electrodes.
 5. The nanomechanical switch ofclaim 1 wherein the cantilever is above spaced apart from the secondelectrode by between 10 and 40 angstroms in the undeflected state. 6.The nanomechanical switch of claim 1 wherein the cantilever member isformed of a refractory metal.
 7. The nanomechanical switch of claim 1further comprising an oxide feature formed on the substrate, on top ofwhich is formed the third electrode.
 8. The nanomechanical switch ofclaim 1 in which the cantilever element is 2000 angstroms in length. 9.The nanomechanical switch of claim 1 in which a vacuum is formed betweenthe cantilever member and the second electrode.
 10. The nanomechanicalswitch of claim 3 in which the lubricating layer is formed of anconductive material.
 11. The nanomechanical switch of claim 3 in whichthe lubricating layer is formed of an insulative material.
 12. Ananomechanical switch comprising: a substrate; formed on the substrate,an emitter electrode including a cantilever element extending from theemitter electrode, the emitter being formed of a material having amagnetic permeability greater than one; a base electrode formed on thesubstrate, at least a portion of the base electrode being beneath thecantilever element; a collector electrode formed on the substrateadjacent the base electrode, at least a portion of the collectorelectrode being beneath the cantilever element and being formed of amaterial having a magnetic permeability greater than one; and a currentsource coupled to the base electrode.
 13. The nanomechanical switch ofclaim 12 wherein current flowing in the base electrode inducescomplementary magnetic fields within the cantilever and the collectorelectrode.
 14. The nanomechanical switch of claim 12 wherein thecantilever is spaced apart from the base electrode by less than 40angstroms when in an undeflected state.
 15. The nanomechanical switch ofclaim 12 wherein the collector electrode is higher, relative the planeof the substrate, than the base electrode.
 16. The nanomechanical switchof claim 12 further comprising a lubricating layer formed atop thecollector electrode.
 17. The nanomechanical switch of claim 12 furthercomprising interconnection conductors connecting the switch with othercircuit elements.
 18. The nanomechanical switch of claim 12 wherein avacuum gap is formed between the cantilever and the collector electrode.19. The nanomechanical switch of claim 12 wherein a noble gas is placedbetween the cantilever and the collector electrode.
 20. Thenanomechanical switch of claim 12 wherein the spacing between the baseand collector electrodes is less than 0.07 micrometers.
 21. Thenanomechanical switch of claim 12 wherein the base collector is formedof a superconducting material.
 22. A logic circuit comprising: aninsulating material; a first pad formed on the insulating material; afirst cantilever element having a first end connected to the first padand a free end extending substantially horizontally over and spacedapart from the insulating material; a second pad formed on theinsulating material and lying at least in part beneath the firstcantilever element; a third pad formed on the insulating material andlying at least in part beneath the first cantilever element; and avoltage source connected to the second pad, wherein the free end of thecantilever element deflects toward the third pad in response to avoltage being applied to the second pad, thus allowing current flowbetween the first and second pads.
 23. The logic circuit of claim 22further comprising: a fourth pad connected to the third pad, a secondcantilever element having a first end connected to the fourth pad and afree end extending substantially horizontally over and spaced apart fromthe insulating material; a fifth pad formed on the insulating materialand lying at least in part beneath the second cantilever element; asixth pad formed on the insulating material and lying at least in partbeneath the cantilever element; and a second voltage source connected tothe fifth pad, wherein the free end of the second cantilever elementdeflects toward the sixth pad in response to a voltage being applied tothe fifth pad, thus allowing current flow between the fourth and sixthpads.
 24. The logic circuit of claim 22 wherein the first pad forms afirst source electrode, the second pad forms a first gate electrode, andthe third pad forms a drain electrode, and further comprising: a secondsource electrode formed on the insulating material; a second cantileverelement having a first end connected to the second source electrode anda free end extending substantially horizontally over and spaced apartfrom the insulating material; a second gate electrode formed on theinsulating material and lying at least in part beneath the secondcantilever element; and wherein the drain electrode lies at least inpart beneath the first cantilever element and the second cantileverelement.
 25. The logic circuit of claim 22 wherein the insulatingmaterial is quartz.
 26. The logic circuit of claim 22 wherein theinsulating material is silicon dioxide formed on a bulk semiconductorsubstrate.
 27. The logic circuit of claim 22 wherein the insulatingmaterial is sapphire.
 28. A complementary pair nanomechanical circuitcomprising: a gate electrode formed on a substrate; an output electrodeformed on the substrate and having a cantilever member integraltherewith, the cantilever member being spaced apart from the plane ofthe substrate and overlying a portion of the gate electrode, thecantilever member having a free end that is deflected from its normalposition to a deflected position in response to an electrostaticattraction between the cantilever member and the gate electrode; asource electrode lying at least in part beneath the free end of thecantilever member, and positioned such that the free end of thecantilever member contacts the source electrode when in deflected fromits normal position; and a drain electrode lying at least in part abovethe free end of the cantilever member, and positioned such that the freeend of the cantilever member contacts the drain electrode when in itsnormal position.
 29. A complementary pair nanomechanical circuitcomprising: a first electrode having formed therewith a laterallyextending cantilever member, the cantilever member having a free endhaving a normal position and a first deflected position in a firstdirection of an axis of motion, and a second deflected position in asecond direction of the axis of motion; a first control electrodepositioned adjacent but spaced apart from the cantilever member in thefirst direction; a drain electrode positioned adjacent but spaced apartfrom the free end of the cantilever member in the first direction; asecond control electrode positioned adjacent but spaced apart from thecantilever member in the second direction; and a source electrodepositioned adjacent but spaced apart from the free end of the cantilevermember in the second direction.
 30. The complementary pairnanomechanical circuit of claim 29 wherein the axis of motion issubstantially parallel to a substrate upon which the electrodes areformed.
 31. The complementary pair nanomechanical circuit of claim 29wherein the free end of the cantilever member deflects in the firstdirection in response to a control voltage being applied to the firstcontrol electrode and moves in the second direction in response to acontrol voltage being applied to the second control electrode.
 32. Thecomplementary pair nanomechanical circuit of claim 29 wherein the firstand second control electrodes are spaced apart from the cantilevermember by a distance that is greater than the distance between thecantilever member and the source and drain electrodes.
 33. An integratedcircuit comprising: a substrate; a power conductor; a ground conductor;an input terminal; a logic circuit comprising a plurality ofnanomechanical switches, at least one nanomechanical switch beingcoupled to said power conductor, and at least one nanomechanical switchbeing coupled to said ground conductor, each nanomechanical switchcomprising: a first electrode; a second electrode a third electrodehaving a cantilever member extending substantially parallel to thesubstrate and extending over the first and second electrodes; and avoltage source coupled between the first and second electrodes, whereinthe cantilever member has an undeflected state when no bias is appliedbetween the first and third electrodes, and a deflected state when abias is applied between the first and second electrodes.
 34. Theintegrated circuit of claim 33 wherein said logic circuit comprises anarithmetic logic unit.
 35. The integrated circuit of claim 33 whereinsaid integrated circuit further comprises a memory array.
 36. Theintegrated circuit of claim 33 wherein the memory array is comprised ofnanomechanical switching elements.
 37. The integrated circuit of claim33 further including a second logic circuit fabricated from MOStransistors.